Transition From Single-Layer to Double-Layer Steps on GaAs(110) Prepared by Molecular Beam Epitaxy

Even though GaAs (110) is the only semiconductor whose surface structure is known with confidence, little is known about its microscopic growth mechanisms. We have used RHEED to study the role of steps in the MBE growth of GaAs on vicinal GaAs(11O) surfaces which were misoriented by less than 2 mrad. After thermally desorbing the initial oxide, 20 layers of GaAs deposited at 700K produced a surface with single atomic-layer steps having an average terrace length of a few hundred Angstroms. Upon annealing to 800K, a slow mass migration occurred producing a surface with one thousand Angstrom average terrace lengths and predominantly double layer step heights. The RHEED pattern was nearly instrument limited at in-phase angles of incidence, with little background intensity and bright Kikuchi lines. Subsequent deposition showed only weak oscillations in the RHEED intensity, in contrast to growth on the (001) surface. The period of the observed oscillations indicates that the layer-by-layer growth involves single-layer steps. Growth of as little as 5 atomic layers on a surface with double steps could not be annealed to give a RHEED intensity as great as the first annealed surface. These measurements reconcile previous LEED results with the oxygen adsorption measurements of Ranke. The results clearly show the dominance of steps in the formation of RHEED streaks.